Solder is a conventionally known material for connecting a semiconductor device to a conductive pad on a circuit board. According to a well known technique, solder bumps can be formed on a conductive pad of a circuit board, a component such as a semiconductor die can be placed thereon, and the solder is then reflown in order to connect the component to the conductive pad. Alternatively, the solder bump can be formed on the semiconductor component, the component can be placed on the conductive pad, and the solder reflown to connect the component to the conductive pad.
Referring to FIG. 1 for illustrative purposes, to form a solder bump on a conductive pad 14 of a circuit board 10, first a solder paste 15 is deposited on a portion of conductive pad 14. As shown in FIG. 1, to define the area that receives solder paste 15, a solder mask 12 may be applied to the top surface of circuit board 10 which includes an opening over conductive pad 14.
Referring to FIG. 2, after depositing solder paste 15 over conductive pad 14, solder paste 15 is reflown by applying heat; i.e. by taking the solder paste to its reflow temperature to form a liquidous. After the liquidous is cooled, a solder bump 17 is formed over conductive pad 14. It should be noted that solder bump 17 has a curved outer surface 19. Curved outer surface 19 is due to the surface tension when the solder is reflown, and becomes more curved as the volume of solder is increased. Thus, to join a component and a conductive pad on a circuit board using the conventional technique described herein the stenciling of the solder on the circuit board (or the component) requires strict adherence to certain tolerances which complicates manufacturing.
U.S. application Ser. No. 10/970,165 discloses an improvement of prior art described above.